JPS62108579A - Manufacture of solar cell - Google Patents

Abstract

PURPOSE:To simplify a process, and to reduce cost by forming an electrode to an antireflection-film coating surface, diffusing and shaping a second impurity region having the same conduction type as a semiconductor substrate onto a first impurity-region removing surface as required and forming an electrode on the first impurity-region removing surface. CONSTITUTION:A breakdown layer in the surface layer of a P-type silicon wafer 1 is removed and the surface layer is smoothed, a wafer 1 is washed and dried, and left as it is in a POCl3 vapor phase atmosphere, POCl3 is permeated and diffused, an N-type high concentration layer 2 is shaped onto the whole surface layer, and a TiO2 film 4 is formed on the light-receiving surface 3 side of the silicon wafer as an antireflection film 11. The silicon wafer is dipped into a sodium hydroxide aqueous solution to remove an N<+> layer on the surface layer not coated with the antireflection film, and Al paste 6 is printed on a surface 5 on the side reverse to the light-receiving surface and baked to shape a P-type high concentration layer 7. Ag paste is printed on the TiO2 film 4 and the Al printing baking surface and baked to form silver electrodes 8, and solder layers 9 are shaped onto the electrodes, thus completing a BSF type solar cell 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a method for manufacturing solar cells. In more detail, the work process has been simplified by applying direct alkaline etching treatment after forming the anti-reflection film. This invention relates to a method for producing a pond II.

(b) Conventional solar cells include those that have only one PN junction between both electrodes (hereinafter referred to as conv type) and those that have one PN junction and other impurity regions between both electrodes (BSF type). There is.

The conventional solar cell manufacturing method has been changed to the BSF type (N÷/P/P
”) as an example and will be explained with reference to FIGS. 8 to 16. 1) After the P-type silicon wafer (1) is subjected to alkali etching to treat the surface (FIG. 8), 2) POCl2
3) Reflection of 5tO2, etc. on the surface to be the light-receiving surface (3) to form an N-type high concentration layer (N"layer") 12J on the entire surface layer of the wafer. Prevention film [11
) (Fig. 10), 4) Cover the light-receiving surface with a masking material such as resist ink or photoresist (Fig. 11), and 5) fluoro-nitric acid (for example, nitric acid: hydrofluoric acid = 3:1).
) and other mixed acids to chemically etch the exposed parts to separate the junctions (formation of N+/P junctions) (Fig. 12), 6)
After peeling off the masking material +121 (Fig. 13), 7) print AI paste (6) on the back side and bake it at 750°C to form a P+ layer (BSF treatment to form a sword) on the surface of the side (14th Figure), 8) Print Ag paste on the first and back sides of the light receiving surface and bake it to form the electrode (8). Figure 15), 9)
A solder layer (9) is formed on both electrodes by dipping (first
Figure 6). Note that (13) shows the obtained BSF type solar cell.

In addition, when manufacturing a conv type (N''/P), it is manufactured by a method that omits step 1) of the above method.

(c) Problems to be solved by the invention However, in the conventional manufacturing method, the above-mentioned 4), 5) and 6
) The process of printing the resist and peeling off the resist requires a considerable amount of time and effort, and there are also problems such as the amount of mixed acid used is quite large, resulting in high costs.

This invention was made to solve these problems, and in particular, it is possible to manufacture solar cells using a simple manufacturing process that does not require operations such as resist printing and resist peeling, and which can reduce costs. It is intended to provide a method.

(2.) Means for Solving the Problems Thus, according to the present invention, a first impurity of an opposite conductivity type is diffused into a semiconductor substrate of one conductivity type to obtain a semiconductor substrate having a first impurity region in the surface layer, After forming an antireflection film made of a metal oxide on one side of the substrate, the first impurity region on the other side is removed by directly subjecting the substrate to an alkali etching treatment, and then an electrode is formed on the antireflection film-covered surface. and a second impurity region having the same conductivity type as the semiconductor substrate is diffused as necessary on the surface from which the first impurity region has been removed, and then a step of forming an electrode on the surface is performed to obtain a solar cell. A method of manufacturing a solar cell is provided.

The most characteristic feature of this invention is that after one surface (light-receiving surface) of a semiconductor substrate is coated with an antireflection film, the substrate is directly subjected to alkali etching to dissolve the first impurity region formed on the surface layer of the other surface. (P-N junction separation).

The above-mentioned antireflection film is relatively stable to alkali treatment, can be formed relatively easily, has good crystallinity, and has a large refractive index, such as T+ 02, S!
An oxide film such as 02 is preferable.

The linear film can be easily formed by a vapor phase growth method (hereinafter referred to as CVD), and the thickness of the formed film is preferably about 800 to 1,000.

The type of alkaline solution used in the above alkaline etching,
The treatment temperature and treatment time are appropriately selected depending on the type of semiconductor substrate and antireflection film used, but the method usually used for surface treatment, that is, relatively high concentration (20 to 50%)
using an aqueous alkali hydroxide solution at a relatively high temperature (80 to 9
A method of dipping at 0℃) is suitable, and the dipping time is such that the surface layer of the semiconductor substrate is dissolved and unnecessary first layer is removed.
A suitable time is to remove the impurity fR region and not to affect the thickness, crystallinity, etc. of the antireflection film coated on the light-receiving surface of the substrate. For example, a P-type silicon wafer is used as a semiconductor substrate, and the anti-reflection film has a thickness of 800 to 1000 T.
When iO2 is used, dipping in a 50% aqueous sodium hydroxide solution at a liquid temperature of 90°C for 0.5 to 1 minute can be mentioned.

Note that the semiconductor substrate of one conductivity type used in the method of the present invention is preferably a semiconductor substrate made of silicon or the like.

Preferably, the surface of the substrate that will become the light-receiving surface is surface-treated in advance. The processing includes a texturing process (anisotropic etching) that makes the surface have dense pyramid-like irregularities, or a process that removes the destroyed layer to make the surface smooth. The above process is performed using a silicon wafer having, for example, a (100) or (511) crystal axis, which is suitable for manufacturing a type of thick Ill battery in which reflection of light on the light receiving surface is reduced.

Diffusion of the first impurity used in the method of the present invention is performed by vapor phase diffusion. For example, when diffusing an N-type impurity into a P-type semiconductor substrate, vapor phase diffusion is performed using POCI 3 as an N-type impurity source. .

The formation of the electrodes used in the method of the present invention and the formation of the second impurity region provided as necessary are performed using materials known in the art (for example, A1 paste, A!+ paste, etc.) and by known methods (for example, , printing, firing, etc.).

(E) Function The surface layer is doped with a second impurity, and the surface layer that serves as the light-receiving surface is coated with Ti 02 , S! When a semiconductor substrate on which an antireflection film made of 02 or the like is directly dipped in a relatively high concentration aqueous alkali hydroxide solution at a relatively high temperature for a short period of time, the antireflection film on the substrate is dipped during this time. The side that does not have any surface directly contacts the above alkaline solution, reacts and dissolves,
The first impurity region formed on the surface layer of the slope is removed.

On the other hand, the antireflection coating is sufficiently stable while the areas are removed by the alkaline etching. That is, according to the method of the present invention, the antireflection film is not substantially etched with alkali and acts as a kind of masking material.

The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereby.

(f) Examples Figures 1 to 7 show BSs manufactured by the method of this invention.
An explanatory diagram of each process of an F-type solar cell is shown.

First, an As-cut P-type silicon wafer (1) (thickness 500μ) was dipped in a 50% sodium hydroxide aqueous solution at a temperature of 90°C for 5 minutes to remove the surface layer of the P-type silicon wafer (1). The destroyed layer is removed and the surface is smoothed (Figure 1). Next, after washing and drying the P-type silicon wafer (1), the wafer was left in a POCI3 (N-type dopant) gas phase atmosphere at 900°C for 60 minutes, and PO
CI 3 is permeated and diffused to form an N-type high concentration layer (N+ layer) (
2) is formed on the entire surface layer (Fig. 2). After that, an anti-reflection film (1υ) and a TiO2 film (4
) is formed to a predetermined film thickness of 800 mm using the CVD method. At this time, the refractive index of the tunica media was 2.3 (Fig. 3). Thereafter, the silicon wafer is dipped in a 50% sodium hydroxide aqueous solution at a temperature of 90°C for about 0.5 minutes to remove the surface N+ layer that is not covered with the antireflection film (Figure 4). . Next, print A1 paste (P-type dopant) (6) on the surface opposite to the light-receiving surface (back surface) (5) and
By baking at ℃, a P wall high concentration layer (P' layer) (to form a sword (Fig. 5)) was formed, and then A(] paste was printed on the Tl0q film (4) and the A1 printing and baking surface to form a layer of 700℃.
℃ to form a silver electrode (8) (Fig. 6), a solder layer (9) is formed on the electrode by dipping to form an 88F type solar cell (K)) (No. 7) by the method of the present invention. Figure) has been completed.

When the electrical properties of the BSF type solar cell (11) obtained by the above method were measured, it showed excellent properties equivalent to those of products produced by the conventional method.

(g) Effect of the invention According to the method of this invention, TiO used as an antireflection film
Films such as 2 and 5f02 are stable in alkaline solutions, while the semiconductor substrate reacts to alkaline solutions, making it possible to easily achieve P-N junction separation by alkali etching. Labor-intensive operations such as ink printing, photoresist coating, and resist peeling are eliminated, simplifying the work process, improving efficiency, and reducing labor costs.

Moreover, an expensive etching solution such as a mixed acid for separating the junctions is no longer necessary, and the overall cost of the solar cell can be reduced.

[Brief explanation of drawings]

FIGS. 1 to 7 are process explanatory diagrams of an example of the method of this invention,
FIG. 8 to FIG. 16 are process explanatory diagrams of the conventional method. (1)...P-type silicon wafer, (2)...
...N"ll!, (3)... Light receiving surface, (4)
...T i 02 li, f5) ...
・Back side, (6)...AI paste, (sword...
...P÷layer, (8)...Silver electrode, (9)...
... Solder layer, (g) ... Solar cell manufactured by the method of this invention, (11) ... Antireflection film, O9 ... Masking material , (13)...
...Solar cells manufactured by conventional methods. Figure 1 Figure 5 Figure 2 Figure 6 Figure 3 Figure 8 Figure 13

Claims (1)

[Claims] 1. Diffusion of a first impurity of an opposite conductivity type into a semiconductor substrate of one conductivity type to obtain a semiconductor substrate having a first impurity region on the surface layer, and a reflective layer made of metal oxide on one surface of the substrate. After forming the antireflection film, the first impurity region on the other side is removed by directly subjecting the substrate to an alkali etching treatment, and then a step of forming an electrode on the antireflection film-covered surface and a step on the surface from which the first impurity region has been removed are performed. A method for manufacturing a solar cell, which comprises, if necessary, diffusing and forming a second impurity region of the same conductivity type as the semiconductor substrate, and then performing a step of forming an electrode on the surface to obtain a solar cell. 2. The method according to claim 1, wherein the antireflection film is made of SiO_2 or TiO_2.